Hector from North Bay, Ontario, tells me that he has just built a new house. He has soffit vents on both side of the house but no gable nor roof top vents. Is this enough?
Simply -- NO.
If there is a strong wind, you would probably get a little air moving through the attic, but most likely just sliding across the insulation and out the other side. The rest of the space will remain unventilated. When there is no wind, there will be no ventilation at all.
Attic ventilation needs to be evenly divided between the top and the soffits so that you always have some air flow, wind or no wind that reaches all parts of the roof and the attic.